Engine exhaust systems utilize hydrocarbon retaining devices, such as hydrocarbon (HC) traps, to retain cold start emissions (HC storing). The retained HCs may be reacted or recirculated into the engine intake system at a later time (HC purging), for example after the exhaust temperature has warmed up sufficiently. Engine exhaust systems may also be coupled to engine exhaust gas recirculation (EGR) systems wherein an EGR flow is used to purge stored HCs from the HC traps. For example, one or more exhaust valves may be used to adjust an amount and direction of exhaust flow through the exhaust treatment system based on whether a storing or a purging operation of the HC trap is desired, or whether an EGR operation is desired. The one or more exhaust valves may be integrated such that the opening of one valve is coupled to the closing of another valve by a common actuator.
However, integrated exhaust valves may have limited flow characteristics. For example, during conditions when it is desired to purge stored HCs into the engine intake by adjusting an EGR flow, it may not be possible to maintain a first exhaust valve closed, to divert exhaust away from the tailpipe, while adjusting the degree of opening of a coupled second exhaust valve to adjust the amount and/or direction of EGR purge flow, using such integrated valve systems. Rather, it may be required to decouple them and use independent actuators. As such, the decoupling of the valves and the use of dedicated actuators may add substantial operating costs. The limited flow characteristics may also affect the efficiency of the exhaust treatment system, thereby degrading the quality of exhaust emissions.
Some of the above issues may be addressed by an engine exhaust system comprising, a first valve, and a second valve coupled to the first valve via a shaft. A first position of the shaft may close the first valve and open the second valve. A second position of the shaft may close the second valve and open the first valve by a first amount. A third position of the shaft may close the second valve and open the first valve by a second, larger amount.
In one example, an engine exhaust may include an integrated exhaust valve system comprising a first throttle valve and a second isolation valve mounted on a common shaft. The valves may be operated by a common actuator through the common actuation shaft. The throttle valve may include a throttle plate enabling the valve to be fully opened, fully closed, or positioned at a wide range of opening angles there-between. The isolation valve may be a ball valve with an inner ball or cylinder having a tunnel there-through, such that flow of exhaust gas through the tunnel may be coupled to flow of exhaust gas through the throttle plate based on the position of the inner ball or cylinder. The throttle valve may be positioned in a first conduit of the engine exhaust, while the isolation valve may be positioned in a second conduit of the engine exhaust, disposed parallel to the first conduit. The second conduit may further include a HC trap upstream of the isolation valve. Each of the first and second conduits may further communicate with an exhaust tailpipe.
During a first condition, for example during HC storing conditions, the actuator may be operated to position the valve system in a first configuration with the throttle valve fully closed and the isolation ball valve open. In this position, exhaust gas may be diverted away from the first conduit (and the throttle valve) into the second conduit (and the isolation valve). Thus, exhaust gas may be routed through the HC trap of the second conduit before being vented to the atmosphere through an exhaust tailpipe. In this way, exhaust HCs may be stored in the HC trap, for example, before a catalyst light-off temperature is reached.
During a second condition, for example during HC purging or EGR conditions, the actuator may be operated to position the valve system in a one of a second or third configuration with the isolation valve closed and the throttle valve partially open. Specifically, in the second configuration, the throttle valve may be open by a first amount, while in the third configuration, the throttle valve may be open by a second, larger amount while the isolation valve remains closed. The first and second amounts may be adjusted based on a desired amount of EGR, a desired amount of purging, a desired HC trap inlet temperature, a desired exhaust catalyst temperature, etc. The second conduit may also communicate with an engine intake through an EGR passage. Thus, when in the second or third configuration, at least some exhaust gas may be diverted to the engine intake via the EGR passage. In one example, during HC purging conditions, an EGR valve in the EGR passage may be additionally adjusted so that at least some exhaust gas is diverted to the engine intake through the HC trap. At the same time, at least some exhaust gas may be vented to the atmosphere following processing in an emission control device. In this way, HCs stored in the HC trap during a previous storing operation may be purged to the engine intake, while at least some exhaust gas is vented to the atmosphere after being processed in the emission control device. In another example, during EGR conditions, the EGR valve may be adjusted so that at least some exhaust gas is diverted to the engine intake while bypassing the HC trap, while at least some exhaust gas is vented to the atmosphere after being processed in the emission control device. In this way, an efficient EGR operation may be enabled using the integrated valve system and without requiring additional EGR system.
In this way, a common actuator and shaft may be used to vary the opening of the throttle valve while the isolation valve remains closed. By enabling a wide range of throttle positions without affecting the isolation valve position, an integrated exhaust valve system may be used to advantageously couple the EGR system with the exhaust treatment system while providing component reduction advantages.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.